Ion-selective Glass Electrodes Research Articles

Composite Ag/AgCl/KCl Screen-Printed Reference Electrode

The drive for automation in multiple industries has generated unmet demand for low-cost, disposable sensors with short response times for routine electrochemical sensing. Glass ion selective electrodes containing a liquid electrolyte have remained the standard for decades, despite their fragile, bulky nature and regular maintenance requirements restricting their suitability for long-term in-situ monitoring. Advances in printing technologies have enabled solid thick film electrodes to emerge as a possible solution to these challenges.Screen printing can be used to mass-produce units of simple, modifiable, and reproducible sensors using minimal materials, increasing portability and reducing fabrication costs. Traditional glass electrode materials are not suitable for printed fabrication, so new materials and designs are required to deliver reliable and robust printed sensors for a variety of industries. While electrochemical sensors can be used to monitor key aqueous environmental indicators, including pH, heavy metals, and oxidation-reduction potential, they often require a stable reference electrode to gain meaningful measurements. Many previous printed electrochemical sensors have relied on a pseudo-reference electrode containing no stabilising electrolyte, however any resultant potential variation can affect measurement accuracy in unknown solutions.In this study, a new screen-printed "true" reference electrode was developed based on Ag/AgCl and a solid composite KCl electrolyte. The electrode lifetime was tested in a 0.1 M K2SO4 solution, and open circuit potential (OCP) stability was tested in H2SO4, KOH, alkali cations (Li+, K+, Na+), halogen anions (F-, Cl-, Br-, I-), KMnO4, H2O2, ascorbic acid, KCl, and standard pH buffers (pH 4, 7, 10). The initial stabilisation and water permeation was monitored via electrochemical impedance spectroscopy (EIS).The observed electrode lifetime in 0.1 M K2SO4 was up to 39 days, with less than 5 mV deviation from the theoretical value (-45 mV vs SCE) and a shelf life of over 1 year. According to the EIS and OCP data, the electrode typically stabilised within 2 hours. In the stability tests, the electrode potential did not deviate more than 10 mV from the theoretical value in the presence of KOH, alkali cations, halogen anions, ascorbic acid, KCl, and standard pH buffers. The electrode was also stable in H2O2 at concentrations up to 0.1 M. On average, the electrode potential was 12 mV below the theoretical value in 10% H2SO4 and was significantly below the theoretical value in 0.1 M KMnO4.The results of this study suggest that this screen-printed reference electrode is suitable for use in electroanalytical systems in most tested chemical environments. The relatively long lifetime and stability of the electrode allows it to be used in a variety of applications, including environmental monitoring, laboratory measurements, and industrial process monitoring, as part of a printed sensor system.

CSIRO SENSEI™ in Situ System for Groundwater Monitoring

Currently, standard electroanalytical multi-sensor systems used in-situ to monitor the chemistry of aqueous systems are based on conventional glass ion-selective electrodes. Issues with these electrodes are common and range from their fragile construction, to fouling of the junction and often reference electrode poisoning. Remote operations, such as mining sites, require new technologies to overcome these challenges, encouraging the development of low-maintenance options for monitoring mineral processes and environmental pollution in-situ.CSIRO is developing a robust and cost-effective solid-state sensor and analytics platform, termed SENSEI™, which includes solid-state electrodes and system electronics embedded directly into the measurement unit. The monitoring system includes CSIRO’s patented pH and reference electrodes together with ORP and conductivity sensors. Third party sensors can be included as part of the unit via MODBUS connection. The all-solid construction of the unit enables operation at elevated pressures and in the presence of external forces, and direct contact of the electrodes with the electronics removes the need for analogue cables, reducing electronic interference.A key feature of the SENSEI™ system is the patented solid-state reference electrode. Due to the issues mentioned earlier, conventional reference electrodes were not suitable in an all-solid system and this led to CSIRO developing a new solid salt-polymer composite reference electrode. The SENSEI™ reference electrode includes an Ag/AgCl reference element embedded in a composite material of crosslinked polyvinyl acetate and KCl. After the initial stabilisation time the potential of the reference electrodes stabilises at -45±5 mV vs. SCE. According to laboratory and pilot-scale experiments, the electrode functions maintenance-free during continuous online monitoring for 9-12 months in aqueous systems, including groundwater and acidic mineral leaching systems.The first large-scale application for the system is in environmental groundwater monitoring of an in-situ recovery operation at Heathgate Resources Pty Ltd. In in-situ recovery mining systems the leaching solution is pumped underground, where it dissolves the metals of the ore deposit, and afterwards pumped back to the surface for post-processing, so proper process control is crucial for a safe and environmentally friendly operation to ensure mining fluids are contained within the mining region. Continuous monitoring of the lateral, overlying and underlying aquifers which ring the mining operation enables quick corrective actions to be taken in the event of possible contamination from a leaching solution. The field trial began in 2019 and will continue until the end of 2020.Figure. A schematic drawing of the SENSEI™ sensor unit. The sensor pack includes solid-state (1) ORP electrode, (2) reference electrode, (3) pH electrode and (4) conductivity/temperature sensor. Figure 1

Potentiometric sensors with chalcogenide glasses as sensitive membranes: A short review

Nowadays there exists a large variety of Ion Selective Electrodes with chalcogenide glasses as sensitive membrane. This short review paper will discuss the development of these sensors for the last almost fifty years. The glass compositions, response modelling, construction methods, parameters evaluation and applications are reviewed. Research breakthroughs and remaining problems on chalcogenide glass Ion Selective Electrodes are discussed.

Development of an improved ligand mimetic calibration system for the analysis of iron(III) in seawater using the iron(III) chalcogenide glass ion selective electrode: A combined mechanistic and analytical study

Further to previous work on a seawater ligand mimetic calibration system for the electroanalysis of iron(III) in seawater using the iron chalcogenide glass ion-selective electrode (ISE), this study utilized alternative blends of synthetic ligands, in order to fine-tune and optimize the calibration response characteristics of this sensor for the electroanalysis of free iron(III) in seawater. Herein, an alternative calibration system (ACS) was derived using a mixture of 10−4M iron(III) chloride, 10−4M ethylenediaminetetraacetic acid (EDTA), 10−3M copper(II) sulphate, 5×10−3M ethylenediamine (EN) and 0.60M sodium chloride yielding a Nernstian response of about 30mV decade−1. The electroanalysis of free iron(III) in seawater using the ACS generated a free iron(III) level commensurate with the predicted organic and inorganic speciation of iron(III) in seawater. Furthermore, electrochemical impedance spectroscopy (EIS), synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy have demonstrated that the surface reaction processes of this membrane in the ACS are comparable to those experienced in a natural seawater matrix. Ultimately, this study demonstrated that the ACS can mimic the surface chemistry and concomitant potentiometric response characteristics of the iron(III) sensor in seawater, enabling reliable electroanalyses of free iron(III) in seawater.

A near edge X-ray absorption fine structure (NEXAFS) study of the response mechanism of the iron (III) chalcogenide glass membrane ion-selective electrode

We have utilized synchrotron radiation-X-ray photoelectron spectroscopy (SR-XPS) and near edge X-ray absorption fine structure (NEXAFS) to demonstrate unequivocally that the modified surface layer (MSL) of the iron chalcogenide glass ion-selective electrode (ISE) comprises a mixture of iron(II) and iron(III) redox states, as proposed in previous theories to explain the mixed electron transfer and ion exchange response mechanism of this analytically important ISE.

Response Mechanisms and New Approaches with Solid‐State Ion‐Selective Electrodes: A Powerful Multitechnique Materials Characterization Approach

AbstractIn modern materials science, there is a plethora of characterization techniques of materials that can provide valuable insights into the fundamental chemical physics of solid‐state devices such as chalcogenide glass ion‐selective electrodes (ISEs). In this paper, electrochemical impedance spectroscopy (EIS), X‐ray photoelectron spectrometry (XPS) and secondary ion mass spectrometry (SIMS) have been used in the elucidation of the mechanistic chemistry of the cadmium chalcogenide glass ISE. Furthermore, in situ synchrotron radiation‐grazing incidence X‐ray diffraction (SR‐GIXRD), in situ EIS/SR‐GIXRD, along with small angle neutron scattering (SANS), can be used to unravel the complex relationship between the nanostructure, bulk electrical conductivity and concomitant electrochemical reactivity of an iron chalcogenide glass ISE. Significantly, exciting preliminary modified atomic force microscopy (AFM) data – utilizing AFM cantilevers with attached microparticles of the copper sensing material jalpaite – demonstrate the tremendous potential of selective force ISE‐AFM in the imaging of important molecular structures such as the copper ion channels of cell membranes in fish gills and/or phytoplankton.

In situ electrochemical impedance spectroscopy/synchrotron radiation grazing incidence X-ray diffraction—A powerful new technique for the characterization of electrochemical surfaces and interfaces

A marriage of electrochemical impedance spectroscopy (EIS) and in situ synchrotron radiation grazing incidence X-ray diffraction (SR-GIXRD) has provided a powerful new technique for the elucidation of the mechanistic chemistry of electrochemical systems. In this study, EIS/SR-GIXRD has been used to investigate the influence of metal ion buffer calibration ligands, along with natural organic ligands in seawater, on the behaviour of the iron chalcogenide glass ion-selective electrode (ISE). The SR-GIXRD data demonstrated that citrate – a previously reported poor iron calibration ligand for the analysis of seawater – induced an instantaneous and total dissolution of crystalline GeSe and Sb 2Se 3 in the modified surface layer (MSL) of the ISE, while natural organic ligands in seawater and a mixture of ligands in a mimetic seawater ligand system protected the MSL's crystalline inclusions of GeSe and Sb 2Se 3 from oxidative attack. Expectedly, the EIS data showed that citrate induced a loss in the medium frequency time constant for the MSL of the ISE, while seawater's natural organic ligands and the mimetic ligand system preserved the medium frequency EIS response characteristics of the ISE's MSL. The new EIS/SR-GIXRD technique has provided insights into the suitability of iron calibration ligands for the analysis of iron in seawater.

In situ synchrotron radiation grazing incidence X-ray diffraction—A powerful technique for the characterization of solid-state ion-selective electrode surfaces

An in situ surface study of the iron chalcogenide glass membrane ion-selective electrode (ISE) in aqueous media has been undertaken using a tandem technique of mixed potential/synchrotron radiation grazing incidence X-ray diffraction (SR-GIXRD) and atomic force microscopy (AFM). This work has simultaneously monitored the mixed potential and in situ surface diffraction patterns of this crystalline glassy material, showing that the observed gradual shift of the electrode potential in the anodic direction is linked to the preferential dissolution of the GeSe (1 1 1), GeSe (1 0 1) and GeSe (1 4 1) and/or Sb 2Se 3 (0 1 3), Sb 2Se 3 (2 2 1) and Sb 2Se 3 (0 2 0) surfaces. Expectedly, these observations are internally consistent with preferential oxidative attack of the crystalline regions of the membrane comprising GeSe and/or Sb 2Se 3, as evidenced by AFM imaging of the electrode surface. Clearly, this work corroborates the results of previous ex situ surface studies on the iron chalcogenide glass ISE, whereby it was shown that alkaline saline solutions have a tendency to alter the surface chemistry and concomitant response characteristics of the ISE.

Continuous flow analysis of iron in zinc electrowinning electrolyte using an iron chalcogenide glass ion-selective electrode: Part I. Synthetic media

It is shown that the iron(III) chalcogenide glass membrane ion-selective electrode (ISE) can be calibrated in continuous flow analysis (CFA) using acidified iron(III) nitrate standards, yielding a 60±3 mV per decade change in activity of Fe 3+ response in the range 10 −7–10 −2 M total iron(III). Extended ageing of the iron(III) ISE in 2 M zinc(II) sulphate did not alter the potentiometric response characteristics of the electrode. Furthermore, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy in the presence and absence of zinc(II) sulphate failed to detect a zinc(II) interference on the iron(III) ISE. CFA/ISE determined activities of Fe 3+ in synthetic zinc electrolyte containing 2×10 −3–2×10 −1 M total iron(III) yielded results falling within ±0.2 log aFe 3+ unit of the corresponding iron speciation data calculated using the minteqa2 program.

Mean activity coefficients of NaCl in (sodium chloride + sodium bicarbonate + water) fromT = (293.15 to 308.15) K

The mean activity coefficients of NaCl in (sodium chloride + sodium bicarbonate + water) were determined experimentally in the temperature range 293.15 K to 308.15 K at four NaHCO3molality fractions (0.1, 0.3, 0.5, and 0.7). The measurements were made with an electrochemical cell, using a Na+glass ion-selective electrode and a Cl−solid-state ion-selective electrode. The experimental values reported by Butler and Huston are found to be higher than those calculated from the Pitzer equation using the existing parameters while the experimental results of this work are close to the calculated values, up to an NaHCO3molality fraction of 0.5. At the NaHCO3molality fraction of 0.7, the experimental data are much lower than the calculated values, implying that the interference of HCO3−on the Na+glass ion-selective electrode can only be neglected up to a molality fraction of NaHCO3of 0.5, an observation which is consistent with that of Butler and Huston.

Sol−Gel Modification of pH Electrode Glass Membranes for Sensing Anions and Metal Ions

To obtain glass membrane electrodes selective for anions and metal ions, pH electrode glass membranes were modified by a sol-gel method using a quaternary ammonium salt and a bis(crown ether). A chloride ion-sensing glass membrane was designed, in which a pH electrode glass membrane was modified chemically by an alkoxysilyl quaternary ammonium chloride. X-ray photoelectron spectroscopy confirmed the chemical bonding of the quaternary ammonium moiety to the starting glass surface, which afforded the first example of glass-based "anion"-sensing membranes. A neutral carrier-type sodium ion-selective glass membrane was also fabricated which encapsulates a bis(12-crown-4) derivative in its sol-gel-derived surface. Both sol-gel-modified anion and metal ion-selective glass electrodes exhibited high sensitivity to their ion activity changes. The present sol-gel modification paves the way for designing glass-based ion sensors with tailor-made ion selectivities toward anions as well as cations.

Continuous flow analysis of mercury using a chalcogenide glass ion-selective electrode

A commercial Hg chalcogenide glass ion-selective electrode (ISE) has been characterized using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, and the compositional data have been used in the fabrication of our own Hg ISE. It is shown that continuous flow analysis (CFA) is suitable for rapid determinations of ultratrace levels of mercury in saline media when used in conjunction with an extrapolation method that predicts the steady-state potential of the Hg ISE by using the initial data following a stepwise change in aHg2+. The CFA technique yields a near-Nernstian response of 28 mV per decade change in aHg2+ in Hg buffers in the range 10−18 to 10−12 M Hg2+. It is shown that the repeatability of the CFA technique in seawater is ±0.03 pHg units, and a seawater matrix effect causes a significant offset and apparent error in the response of the Hg ISE relative to Hg buffer standards. Standard addition CFA may be used to compensate for the seawater matrix interference. © 2000 John Wiley & Sons, Inc. Lab Robotics and Automation 12:194–199, 2000

Activity Coefficients of HCl in the HCl + NH4Cl + H2O Systems at 298.15 and 313.15 K

Using the ion-selective electrode method with a concentrated electrolyte solution added continuously, the mean activity coefficients of HCl in the HCl + NH4Cl + H2O system were experimentally measured at 298.15 and 313.15 K and at five molality fractions of NH4Cl (y2 = mNH4Cl/(mHCl + mNH4Cl) from 0.1 to 0.9. The measurements were made by an electrochemical cell using a H glass ion-selective electrode and a chloride solid-state ion-selective electrode. It was found that the influence of NH4+ on the H glass ion-selective electrode could be neglected up to 1.3 mol·kg-1, and this pair of ion-selective electrodes was suitable for determining the activity coefficients of HCl in the system. A new set of Pitzer mixing parameters, correlated from the experimental results, was used to calculate the activity coefficients for HCl in the system from 293.15 to 313.15 K up to 3.0 mol·kg-1.

Continuous flow analysis of iron (III) in seawater using a chalcogenide glass ion-selective electrode

Continuous flow analysis (CFA) is suitable for rapid and reliable determination of free FeIII in organic-free, UV-oxidized seawater when used in conjunction with an extrapolation method that predicts the steady-state potentials of an FeIII chalcogenide glass ion-selective electrode (ISE) by using initial data associated with a step-wise change in aFe3+. It is shown that the CFA technique yields a Nernstian response of a 30 mV per decade change in aFe3+ in saline citrate buffers in the range of 10−22 to 10−1 M Fe3+. Validation of the CFA technique in organic-free, UV-oxidized seawater has demonstrated that the response of the FeIII ISE is internally consistent with the well-known inorganic speciation equilibria occurring in natural seawater. © 1999 John Wiley & Sons, Inc. Lab Robotics and Automation 11: 284–288, 1999

Ion-selective field-effect transistor and chalcogenide glass ion-selective electrode systems for biological investigations and industrial applications

In this paper the fabrication and application of two different modern potentiometric solid-state chemical sensors, namely, chalcogenide glass ion-selective electrodes and field-effect transistor-based sensors, are described. Examples of their use in industry, waste water analysis and biomedical treatment are discussed.

Some Recent Approaches to Micro- and Ultramicro-Elemental Organic Analysis

Automatic instrumentation has been developed for the microdetermination of various elements in organic samples ranging from 2 to 3mg. The author has devised a microanalyzer for carbon, hydrogen and nitrogen which embodies a pump system for collecting the combustion gas; this device operates on the principle of thermal conductometry for determining the three elements. The pump system is also useful for the microdetermination of organic oxygen in collecting equivalent carbon monoxide, which is then determined by infrared photometry. Organic halogen and sulfur compounds are mineralized in the conventional oxygen flask combustion and the resulting halide and sulfate ions are titrated potentiometrically with standard silver nitrate or barium chloride by means of an ion-selective glass electrode for getting the end point. Equivalence points are characterized by extremely sharp points of inflection; i.e. short lengths on the steeply rising sections of the titration curve. Ultramicrodetermination of elements in 0.5mg organic sample or lessare vital in the field of biochemistry. Dry combustion in a sealed tube has been proposed to minimize the blank value and to eliminate loss of reaction products. Accurate determination of nitrogen and later of carbon, hydrogen and nitrogen simultaneously has become possible. This approach has been further extended to the determination of halogen and sulfur.

The Stability Constants of Some Benzo-15-Crown-5 And Naphtho-15-Crown-5 Derivatives

Abstract The stability constants for the complexes of several benzo-15-crown-5 and naphtho-15-crown-5 derivatives containing various substituents in the aromatic ring have been determined in methanol. The potentiometric method with glass ion-selective electrodes has been employed. The stability constants have been compared to the selectivity coefficients (log kpot K,Na ) of membrane electrodes based on the mentioned compounds. No significant relationship has been stated.

Applications of Indicator Electrodes in Evaluating Reactivities of Ions in 1,3‐Dioxolane as Solvent

The response of indicator electrodes for hydrogen, silver(I), and fluoride ions in 1,3‐dioxolane (DXL) as solvent was evaluated. One result was that different classes of reactive impurities in DXL could be detected and determined over wide concentration ranges by adding these ions as probes and monitoring their activities with indicator electrodes. The relative strengths of a number of acids and bases were determined potentiometrically with the hydrogen ion selective glass electrode; this electrode also responds strongly to lithium ion in DXL. Approximate absolute values of dissociation constants were obtained by calibrating the hydrogen ion selective electrode with trifluoromethanesulfonic acid (TFMSA) buffers. Approximate values of the overall dissociation constants of TFMSA and several other acids were determined conductometrically. While a wide range of basicities can be attained in DXL, the range of acidities is severely limited by acid‐catalyzed polymerization of the solvent.

The use of glass ion-selective electrodes for thermodynamic studies on electrolyte solutions 1:1 in water-organic solvent systems: Studies in the water-THF system

The EMF of the cell glass electrode (Na)¦NaCl¦AgCl,Ag in water-tetrahydrofuran (THF) mixtures containing 0, 2.5, 7.5, 10, 15, 20, 25, 30 mol% THF has been measured within the temperature range 293.15–308.15 K. Standard EMF and thermodynamic functions of transfer of NaCl (Δ GXXX t, - TΔ S tXXX,Δ H tXXX) from water to water-THF mixtures were also determined. The values obtained have been compared with the corresponding values obtained by other authors. The possibilities of using cation-selective glass electrodes for thermodynamic studies on electrolyte solutions in systems containing aprotic solvents-water mixtures are evaluated including a critical review of the opinions of other authors.

New solid-state ion-selective electrodes — Sensors for chemical analysis of solutions

From the historic point of view one can consider chalcogenide glass ion-selective electrodes (CGISEs) and ion-selective field effect transistors (ISFETs) as new solid-state sensors for chemical analysis. The paper describes the development of the sensors, the methods of investigation, analytical properties and the sensing mechanism of CGISEs and ISFETs.